based on AI ... say (1.5g/hr x 128 ounces / 60 minutes) x
3 running minutes shoud produce the
9.6 ounces of fuel at low pressure
AI said....
A mechanical fuel pump on a
1976 9.9 HP outboard (whether it's an Johnson or Evinrude two-stroke) doesn't produce much pressure, but it does produce more flow than the engine actually consumes.
Typical values are:
- Pressure: about 2 to 4 psi (3 psi is very common).
- Flow: approximately 1 to 2 gallons per hour (3.8 to 7.6 L/h) at idle cranking speeds, increasing with engine RPM.
One caution: if you disconnect the fuel line from the carburetor, the engine will eventually stop because the bowl empties. On a 9.9 HP at idle, that's usually only
a minute or two, not necessarily a full three minutes. That's normal. You can still calculate the pump's output by measuring the fuel collected during the actual run time.
Based on everything described over the last few days, I'd rank the likely causes as:
- Weak or sticking inlet needle/seat or float problem (most likely).
- Weak fuel pump (to be confirmed by your flow test).
- Restriction between the pump and carburetor (collapsed hose, blocked fitting, debris).
Your flow test is a good next step because it will tell you whether the pump is actually delivering the volume it should under real operating conditions. If it is, there's little reason to suspect the pump, and attention should shift to the carburetor inlet system.
